The airplane collided with terrain during takeoff at 1727 Pacific time. The airline transport pilot captain, commercial pilot first officer and flight engineer sustained minor injuries. The converted aerial refueling tanker sustained substantial damage to its wings, fuselage and empennage from impact forces and a post-crash fire. Visual conditions prevailed. At about 20 feet agl, the number two (left inboard) engine throttle lever slammed back to the idle position. The airplane stopped climbing, and the captain adjusted the pitch slightly down to hold V2 speed. Witnesses observed the airplane lift off, and something shiny go up and over the left wing. They also observed a fireball on the left side of the airplane. The airplane began to drift left and descend. The captain lowered pitch slightly and leveled the wings just prior to the airplane contacting the runway. He informed the crew members they were going to put the airplane back down, placed the throttle levers in the idle position and activated the speed brakes. The airplane departed the left side of the runway surface; the crew reported a couple of impacts and then one final violent impact prior to the airplane coming to rest in a wetland marsh. The crew opened the left main cabin door and deployed the slide. They exited into the mud, and made it to dry land and away from the burning wreckage.